1. Field of the Invention
The invention relates to a buoy for use in loading or unloading of a flowable medium, especially oil, the buoy at its lower end being arranged for connection to at least one transfer line and further is arranged to be introduced into a submerged downwardly open receiving space in a floating vessel, and the buoy in operation forming a transfer connection between the transfer line and a tube system on the vessel.
2. Background Information
There are previously known various buoy structures of the type which, in operation, is introduced into a submerged downwardly open receiving space at the underside of a vessel. As an example, reference may be made to U.S. Pat. No. 4,604,961 (corresponds to NO patent specification No. 167,906). This patent shows a vessel having a releasable mooring system wherein the vessel has a through-going deck opening in a central region of the vessel, the lower part of the through opening forming the submerged receiving space for a mooring element in the form of a submerged buoy. In the receiving space there is arranged a rotating body (turret) which is rotatably mounted in the hull of the vessel and is designed for receipt and attachment of the mooring element, the latter to this end being provided with a hydraulically actuated locking mechanism for attachment to the rotating body. Further, the vessel is provided with a derrick for the lowering of a retrieval string having a retrieval connector at its lower end for interconnection with the mooring element, so that this may be pulled up and into the receiving space. The interconnection is obtained in that the mooring element is provided with a conical centering receptacle having a socket arranged at the bottom wherein the retrieval connector may be received and secured, e.g. by means of a bayonet lock. The lower end of the retrieval string preferably is provided with sonar and TV equipment to ensure positioning of the retrieval connector in the centering receptacle.
Said rotating body, which is mounted in the hull of the vessel, allows the vessel to turn in relation to the anchored buoy also after establishment of the connection, under the influence of e.g. wind, current and waves. Since the rotating body is attached to the vessel under water, this requires divers for inspection and minor maintenance. Major maintenance requires docking of the vessel. Because of the fact that the rotating body is mounted to the vessel, there arise large frictional forces which are to be overcome by torques from the mooring element. These torques are relatively large due to the large outer diameter of the rotating body, and this results in correspondingly large loads. Further, it may result in uncontrolled rotation of the system because of large inertial forces, so that it becomes necessary to use a braking system for retaining the rotating body. In case of desired rotation the braking system is then released, and the rotating body is rotated in a controlled manner by means of active drive.
Further, the known system has a small ability to absorb moments caused by the horizontal mooring forces, something which results in a substantial risk for jamming actions in the mounting arrangement.
The hydraulically actuated locking mechanism which is arranged on the mooring element requires divers for connection of the control hydraulics. Diver operations in connection with connection and disconnection render the use of the system as a transport system impossible, when using shuttle tankers. Further, there is a big risk for faulty operation and damages in case of uncontrolled disconnection. In case of breakage of the hydraulic system there is no possibility for the connection of a back-up or auxiliary device.
It is an object of the invention to provide a loading/unloading buoy which makes it possible to carry out connection and disconnection between vessel and buoy in a quick and simple manner, even in bad weather.
Another object of the invention is to provide a buoy which may remain connected to the vessel in all weathers, a quick disconnection being able to be carried out if a weather limitation should be exceeded.
A further object of the invention is to provide a buoy giving a small diameter of the support means enabling turning of the vessel, so that there is obtained a small rotational resistance and a small rotary mass, and consequently no need for braking or active control of the rotary system.
A still further object of the invention is to provide a buoy which has a relatively simple and inexpensive construction, which gives a simple installation and dismantling, and which in addition gives the possibility to carry our repairs and replacement of parts on board the vessel, without disconnection of the buoy.